I. Field of the Invention
This invention relates to an aromatic polyester composition. More particularly, this invention relates to an aromatic polyester composition and preparation method thereof, which has excellent mechanical properties such as impact strength, which is excellent in flowability and residence stability in molding, and which has excellent hydrolysis stability, resistance to thermal cycling and weatherability.
II. Description of the Prior Art
Aromatic polyesters represented by polyethylene terephthalate and polybutylene terephthalate are widely used in electric and electronic parts and automobile parts because of their excellent properties. However, aromatic polyesters have intrinsic drawbacks in that they have tendency to decompose during molding and have low hydrolysis stability. Further, as an automobile part, it is increasingly important that the mechanical properties of the automobile parts are not degraded after thermal cycling is repeated. However, since aromatic polyesters have poor resistance to thermal cycling, their use is restricted when used as an underhood part of an automobile. As to the improvement of the hydrolysis stability, it has been proposed to add an epoxy compound or an oxazoline compound to the aromatic polyesters. In particular, the method disclosed in Japanese Patent Disclosure (Kokai) No. 82148/80, in which a divalent epoxy compound such as diglycidyl terephthalate is added is relatively more excellent than other methods since the improvement in the hydrolysis stability is greater than those obtained by other methods. However, the resin composition obtained by this method has a drawback in that the flowability and residence stability during molding are extremely poor. To improve the hydrolysis stability without degrading the flowability during molding, it is disclosed in Japanese Patent Disclosure (Kokai) No. 87452/82 that a monovalent glycidyl ester compound is added to the aromatic polyesters. However, by this method, the improvement in the hydrolysis stability is small and the heat-aging resistance is poor, so that the method is not satisfactory.
As to the improvement in the resistance to thermal cycling, Japanese Patent Disclosure (Kokai) No. 285947/87 discloses a method in which an epoxy group-containing copolymer and a rubbery graft-polymers are added. However, this method has a drawback in that the flowability of the resin during molding is lowered and the hydrolysis stability is low.